Wave antenna



May 13, 1930. s, HQYT 1,758,044

WAVE ANTENNA Filed Jan. 22. 1926 r 2. Sheets-Sheet 1 IN VEN TOR A TTORNE Y May 13, 1930. R. s. HOYT 1,758,044

WAVE ANTENNA Filed Jan. 22. 1926 2 Sheets-Sheet 2 IN VEN TOR A TTORNE Y Patented May 13, 1930 Miran 11s Tamas PATENT EQIFFICE RAY S. HOYT, OF RIVER'EDGE, NEWJERSEY, A$SIGNOREO AMERICAN T-ELEPHONE AND TELEGRAPH COMPANY, A CORPORATION Y,QBK

WAVE ANTENNA .Anph ati-onfiled Jan a y. ,:19 S niahNo. 83,1 18- An object ofmy inventi-on-isto provide improved methodsan'd apparatus tor radio reception on a wave antenna. Another-0bject is'to providefor an improved wave antenna of'flexible design for directively selective radio reception. Other objects are to improve the attenuation characteristic in the designaof awave antenna,an'd to tacilitate making the antenna of effective length. All these objects-and others will become apparent in connection withthe following disclosure of examples (if-procedure in the practice of my invention. It will be understood that this specification relates to-these examples and thatthe invention will be defined in the appended claims.

Referring to the drawings,Fig. 1 is a diagrammatic elevation of a comparatively simple wave antenna. Fig-'2 is a diagrammatic elevation of a wave antenna with shunts according to-my invention. Fig. 3 is a diagram showingone of the shunts of Fig; 2 in more specific'form. Fig. 4 is a diagram for a two conductor wave antenna, providing for return signal currents .onithe circuit of these conductors, and Figs. 5itozl0 inclusive are sketches illustrating various shunt load arrangements for a twowire-antenna.

The'horizontal conductor 21 of Fig. 1 is carried on poles above the ground and eX- tends a distance comparable to one or several wave-lengths of the waves desired to be received, and in the direction of these waves as indicated by the arrow '22. .At theiront end (toward the distant transmitting station) the line 21 is grounded throughtheimpedance WV o'f valueequal to'the characteristic impedance of the line. At the distant or back end the line is grounded through receiving apparatus of impedance valueZ. V

The incoming electric wavesare ordinarily regarded as comprising advancing vertical lines of electricforce in zones alternately directed up and down. More accuratelythese lines offorceare inclinedslightly forward as represented by thelines 23 inFig. 1. Accordingly each such line has a component alongthe-conductor, and if the velocity of propagation along the conductorissubstantially the same as the incoming'radio waves,

the effect in the conductor will'be cumulative and a wave of current 'willbuild up along the conductor and be of substantial e'flect on arrival at the receiver Z. 011 the otherhand,

waves from the opposite direction as repre-.

sented by the dotted arrow 22,1will have-their cumulative effect only at W, and: since this has the characteristic.impedanceyaluathere will be no reflection at'W* by which reflected waves could reach the receiver Z.

In Fig. 2 I. have shown shunts each ofadmittance value Y at equal distancesD along the line. The object of the shuntloadingfis to alter the characteristics ofthewave antenna by increasing its velocity of phase propagation and by decreasing its attenuatlon constant.

In any actual wave antenna, the unavoidable resistance in the antenna wire and in the earth, and the shunt leakage from the antenna wire to earth, always cause attenuation, and also decrease the velocity ofphase propagation. By means of the shunt'loading of the present invention, these effects of re sistance and leakage can be partly or largely compensated: for the attenuation can be substantially decreased, and the velocity of phase propagation can be greatly increased-even to an extent of over-compensation.(thatis, the velocity of phase propagation can be made to exceed the value" it would have in the absence of resistance andleakage).

This possibility of inereasingthe velocity of propagation renders the wave antenna morefiexible in design to meet specified requirements. The possibility of decreasing the attenuation permits the use of a wave an- 'tenna of greater length and hence of greater ly the wire contributes to the attenuation U much less than does the earth.

I shall employ the formulas for theatten- .uation constanta'and the velocity of phase propagation '0.

If y denotes the propagation constant, then a where i= 1, and ,8 is the so-called phase constant or wave-length constant, related to the velocity 'v in accordance with the equation m denoting 211- times the signaling frequency f.

It will now be shown how 12 and a depend on the shunt admittance of the wave antenna; and thence how the shunt admittance can be modified, in accordance with this invention, in such a way as to increase a and decrease on.

To begin with, consider the non-loaded wave antenna of Fig. 1 having, per unit length, a series impedance R +21 and a shunt admittance G-l-z'U R thus being the series resistance, X the series reactance, G the shunt conductance, and U the shunt susceptance.

a ,8 =RGXU (4i) 2a8=RU+ GK (5) To solve these for ,8 and a we may square both sides and add, thus getting (a 'i-B (RGXU) (RU-FGX) whence a +fi /(RGXU) (RU+ GXV 7 the sign being employed because 08-1-8 is necessarily positive. Next, by subtracting and adding (4) and (7), We get On extracting the square roots of these equations we would get two values for a and two for ,8, one being positive and the other negative for each. In the case of a, only the positive value is physically applicable; but 8 is not physically restricted to positive values, in the case of a loaded wave antenna. Since only positive values of 0c are to be considered, Equation (5) shows that 8 is positive or negative according as R U GX is positive or negative, respectively; this is also apparent from the lastform of (3), since the complex quantity o+a',8 is restricted to the positive real half of the complex plane.

Regarding the sign of 8, it may be remarked that, of course, R and G are always positive and that for a non-loaded Wave antenna X and U are positive; and hence that ,8 is positive for a non-loaded wave antenna. For a Wave antenna having no series loading, X would be positive, but U could be rendered negative by means of suitable shunt loading; and then 8 would be negative if U were made algebraically less than GX/B.

In the limit, when R/X and Gr/U are zero, on is zero and 8 and e have the values [3 and '0 such that the sign being or respectively, accord ing as the sign of RU+ GX is+ or in the limit. (For a non-loaded Wave antenna, ,8 and '0 are always positive.)

Strictly, the foregoing Formulas (3), (11) pertain to a wave antenna whose parameters (R, X, G, U) are smoothly (uniformly) distributed; but the formulas are good approximations when some or all of the parameters are periodically distributed, as in the case of any periodically loaded antenna, provided the spacing D of the loading elements is short compared with the wave-length of the signal propagated on the wave antenna. VJith this proviso, the formulas will be applied to the shunt loaded wave antenna (Fig. 2) exemplifying my invention, in which the loading is periodically distributed. The desired characteristics of the loaded antenna are capable of a certain amount of adjustment by adjusting the spacing, and furthermore some economy is evidently attainable by increasing the spacing. In case it should be desired to employ a load-spacing which is not small compared with the wave length, it would, of course, be necessary to employ the rigorous formulas for a periodically loaded antenna.

It will be recalled that the object of the shunt loading of this invention is to alter the characteristics of the wave antenna, by in creasing its velocity of phase propagation and by decreasing its attenuation. That this object can actually be attained by means of shunt loading will now be shown by aid of the foregoing formulas for ,8 and or, together with the relation o=w/8.

It should be noted that the only parameters that can be afiected by any shunt loading are the shunt leakage G and the shunt susceptance U, making up the shunt admittance G+iU. The effects of varying G and U will now be considered separately.

Formula (9) shows that decreasing Gr always decreases on, for all positive values of G.

The nature of the dependence of 8 on G is not so readily perceived, but can be deduced it can not even be reduced to zero.

from the following considerations: Equations (3) and (8) each show that fi w tor G w and for G w and that B =O for G UR/X. Furthermore, if (8) is solved for G in terms of ,8 it is found that for every value of ,6 there are two and only two values of Gr. Consequently B passes through only one eXtremuIn, whichv is the zero value, when G ranges from co to co. Thus, when G UR/X, decreasing G always decreases [3 and hence decreases ,8: but when 6 UR/X, decreasing G always increases B and hence decreases 8 (algebraically). Thus, whenG decreases from w to w, ,3 decreases from co to w steadily; that is, the slope of ,8 as function of G is always positive. This can'be verified by means of the derivative of ,8 with respect to G,

16% 6 (1G 8 1+U /G together with the fact that B is positive when G UR/X and negativewhenG UR/X. Finally, from the relation o=o/B, it is seen that o is positive when G UR/X, and is negative when G UR/X; when G decreases from x to UR/X, o steadily increases from 0 to +00; and when G de creases from UR/X to 00, o steadily increases (algebraically) from co to O.

In application it must be noted that G is physically restricted to positive values. Hence,sinceochangessignwhen G UR/X and since X is positive for a wave antenna havingno series loading, it is seen that U must be made negative (by some sort oi shunt loading) it it is desired to make a infinite or to make o negative by adjustment of G. So long as U and X have a common sign, '0 is positive and increases steadily with decreasing G (though. 2; does not become infinite) thus, the result of decreasing G is to decrease oz and to increase 4) simultaneously. In particular, this is true for a n0n-loaded wave antenna, because then U and X have a common sign, both being positive.

However, there are practical restrictions to the alterations attainable by reducing G; for not only can G not be made negative but There is no such limitation on the susceptance U; and it will next be shown that, by suitably adjusting the susceptance U, by means of shunt loading, 22 can be greatly increased; and that or can be decreased (subject to a certain limitation).

The nature of the dependence of B on U, and hence of Q) on U, can be deduced by arguments analogous to those above pertaining to-the dependence of B on G. It is thereby found that, when U decreases from w to -w, [3 decreases steadily from +co to 00, passing through the value zero when U GX/R. Hence, from o=w/,8, it is seen for U co and for U oo. Furthermore,

for every value of a there are two and only two values of U. Consequently a and hence 0:, passes through only one eXtremum, which n is a minimum, when U ranges from co to w. The location and value of this minimum of or can be determined by means of the derivative of a with respect to U,

X and 0: being positive, this equation shows that a is a minimum when U=GX/R and thence shows that the minimum value, say 0:", of 0c is Thus, when U decreases from co to GX/R, a decreases steadily from 00 to /RG; and when U decreases from 6 X /R to 00, or increases steadily from 'v RG to on. By (14:), the minimum value a of or decreases with decreasing G; thus, it is usually desirable tomake G as small as practicable. Itmay be remarked that, for a wave antenna having no series loading,the minimum of on occurs at a positive value or" U, since X is positive for such a wave antenna. Moreover, for a non-loaded wave antenna, U/G would usually be greater than X/B and hence U greater than GX/R. Thus the adjustment or" U to the particular value GX/R requisite for minimizing a would require reduction of U: this reduction of U can be accomplished by means of shunt loading as herein disclosed.

It is desirable to know the value '0 of o and the value ,8" of [3 corresponding to the minimum value a of 0c. ,8 can be found from (8) by substituting U=GX/R therein, and then 4/ can be found from (2) thus W B/W Thus, 0 increases with decreasing Gr; while, by (14), u always decreases.

Comparing (16) with (11) shows that where, it is to be noted, the parameters U, G, X, R are those of the original wave antenna and hence may have any physically possible values. But, as already remarked, for a nonloaded wave antenna U/G would usually be greater than X/R: hence, after a has been minimized by reduction of U to the particular value GX/R, by means of the shunt loading as herein disclosed, the velocity ratio of U that would meet the specification, since (18) involves only an even power of 1),.

lVhen the attenuation constant a is to have a specified value m the requisite design formula for the total susceptance U =U+ U (per unit length) is obtainable by replacing 0 and U in equation (9) by (1 and U respectively, and then solving for U2. It is thus found that '2)/'21 would exceed unity; thus the present invention enables the reduction of 2) caused by R and G to be even more than compensated by reduction of U, and at the same time enables the attenuation constant 01 to be reduced.

Since a; changes sign when U =-GX/Zi, and since X is positive for a wave antenna having no seriesloading,it is seen that U must be made negative (by some sort of shunt loading) if it is desired to make 41 infinite or to make 4) negative. So long as U is positive o is positive and increases steadily with decreasing U, though v does not become infinite. But it will be recalled that or is a minimum when U GX/R, and hence that decreasing U increases on so long as U is than GX/R. Finally, then, it is seen that, so long as U is greater than Gal/R, decreasing U decreases 0c and simultaneously increases 1). There is no limit to the amount by which 11 can be increased by decreasing U, but there is a practical restriction set by the increase occurring in the attenuation when U is less than GX/R.

There will next be furnished general design-formulas for calculating the requisite susceptance U to be furnished by the shunt loading, per unit length; these formulas will correspond to three specifications, as follows: the phase velocity 1; to have a specified value; the attenuation constant a to have a specified value; in particular, the attenuation constant a to be a minimum.

\Vhen the phase velocity v is to have a specified value '0 and hence B a corresponding value ,8 u the requisite design-formula for the total susceptance U =U+ U (per unit length) is obtained by replacing U and B=w/o in Equation (8) by U and ,8w='v respectively, and then solving for U It is thus found that Both values of U represented by this formula are physically applicable, and will yield the same specified value 0: of a; but they do not yield equal values of oa fact which constitutes a ground of choice between the two values of U In particular, when the attenuation constant a is specified to have a minimum value, namely by Equation (14), then the requisite value for U is U arm 21 as is found by substituting in (19) the particular value of a represented by (20).

There will next be disclosed a particular type of shunt loading for decreasing the sus ceptance U, so as to increase 4} and decrease or. This particular type of shunt loading consists of shunt inductance (Fig. 3) and thus possesses the negative susceptance requisite for neutralizing a portion of the positive susceptance U of the original antenna, so that the resultant susceptance will be less than the original. Let L, denote the load inductance per unit length, and U its susceptance; then where, as before, 0) denotes 2w times the signaling frequency The original susceptance belng C denoting the capacity of the Wave antenna per unit length, the resultant susceptance U U U has the following ratio to U, namely X 2 2 4 2 U2 w Of the two values of U represented by (18), the algebraically larger or the algebraically smaller value is to be chosen according as the specified value '0 of '0 is positive or negative, respectively; if only the absolute value of '0 were specified, there would be two values This shows that U can be made as small as may be desired by suitably choosing L Thus U =O when L 1/w 0. U can even be made negative, but this would have the undesirable eifect of unduly increasing the attenuation constant a, a being a minimum when Since L denotes the requisite inductance per unit length, if uniformly distributed, the requisite inductance L of each loading element is L =DL (26) D denoting the load-spacing chosen.

Equation (24) can be written in the more significant form 1;,=1 er a) where is the signaling frequency, corre sponding to U and U and f is the anti resonant frequency of C and L in parallel,

that is f =1/27r1/0L (28) Equation (24) can be written also in the form U2 iCDO where U =0(11/w UL (30) is the effective shunt capacity of the loaded Wave antenna, per unit length. Thus C is less than C; that is, the result of the loading is to decrease the effective capacity of the wave antenna, and thereby increase the velocity of propagation '0, since i) is approximately equal to the reciprocal of the square root of the product of the capacity and the inductance. This conclusion is evidentally consistent with the foregoing conclusion deduced from a consideration of the susceptance U The vertical component of the impressed electric field (represented by the lines 23 in Fig. 1), acting on the shunt loading elements,

produces currents which complete their circuits through the wave antenna and thus (after undergoing attenuation) contribute to the current in the instrument at the receiving end. The question arises whether the contribution may alter undesirably the directional selectivity of the wave antenna. An investigation to determine the order of magnitude of the current contribution in question. and its dependence on the angle of incidence will sh ow th at while the contrdiution referred to will ordinarily be enough to be noticeable, it-will not ordinarily be enough to be'ha'rmful. Fig; 4 shows 'aftw'o' Wire WaVe'antenna, so arranged that the receiving apparatuscan be located at the front end, the end nearesa the transmitting station from which it is desired to receive. Thefradiowave'sinthe direction-22 affectt-he two wires alike and build up in them a wave of 'ele'ctriccurrent that discharges to ground atlthe distant end through the transformer winding'ac thus'inducing in the two-'wire circuita circulating current which, transrn'itted to -the front end is inductively effective on the receiver. Waves from the undesired direction22 build up alike in the-two conductors, andhe'n'ce their effect on the receiverj27 is neutralized in the transformer at'the front end; 'and the impedance W has the characteristic impedance value, so there is no reflection.

Fig. 5 shows a symbolic-shunt loadfora two wire antenna; However; this afiords a path across from oneconduc'tor to theother through the two impedances, and thus tends to weaken the return ignalturrentfltathe front end receiver. FigL-G shows thejcase' where the grounded impedances are inductances-with the addition of a condenserin parallel with the cross path and of such value as to make the entire shunt path across the conductors anti-resonant and hence of very high impedance to the signaling frequency. Fig. 7 shows the grounded shunt connected to the midpoint of a cross inductance of high impedance value; thus the inductance is neutralized to the waves built up by the radio waves, but is fully efiective against the return signal waves. By the addition of a condenser in parallel with the cross-inductance as shown in Fig. 8, and making the combination antiresonant to the signaling frequency, the cross impedance is increased. In Fig. 9, a 1: 1 transformer is interposed and its midpoints connected together and also connected to ground through the desired impedance shunt. The effect is the same as for Fig. 7 and in addition by winding the coils in the proper directions the effect of a transposition of the conductors is obtained, thus making Fig. 9 correspond to Fig. 10 rather than Fig. 7. Transposition is desirable to neutralize interference and for the further reason that if the normal to the wave front has its horizontal component of direction oblique to the direction of the wave antenna then there will be a difference of phase in the two conductors which would cause a circulating current around the circuit thereof.

The velocity of the waves generated in the conductors by the radio waves will in general be less than the velocity of the radio waves, and this difference of velocity may be referred to as a lag value compared to the veloc ity if the radio waves.

I claim 1. In a two wire wave antenna, shunt paths to ground from both wires at points along the length of the antenna, and means to make the resultant paths across the conductors at these points of high impedance.

2. In a two wire wave antenna, shunt paths to ground from both wires at points along the length of the antenna, and means comprising these shunt paths at least in part and forming anti-resonant loops across the conductors at said points.

3. In a two wire wave antenna, shunt inductance susceptance paths to ground from both wires at points along the length of the antenna, and cross connected condensers combined therewith to make the complete cross paths anti-resonant.

4. In a two wire wave antenna, shunt inductance susceptance paths to ground from both wires at points along the length of the antenna, at least part of the inductance being neutralized from the wires to ground but elfective across the wires.

In testimony whereof, I have signed my name to this specification this 21st day of J anuary, 1926.

RAY S. HOYT. 

